Encapsulated fuse structure for polyphase circuits



May 9, 1967 Filed Jan. 26, 1965 5 Sheets-Sheet 1 F|G.|. F|G.2.

/ f 10 ,10 5 s1 1 E I1 I 8 I i 8 i A 3 r 1 o o o o 50 0 o o o 5u 5b o a o o P. c. HITCHCOCK 3,319,027 ENCAPSULATED FUSE STRUCTURE FOR POLYPHASE CIRCUITS O O O O 7 g .0 2 a g W A 5. 8 W A C I a 2 9 g 5 INVENTOR= PM} WM BY RNA/NAM ATTORNEY II/I) P. C. HITCHCOCK May 9, 1967 BNCAPSULATED FUSE STRUCTURE FOR POLYPHASE CIRCUITS 3 Sheets-Sheet z:

Filed Jan. 26, 1965 FIGQ40.

.Imlll I NVENTOR r c abmm BY 4M XTTORNEY ILFIIIIII ML T United States Patent Office 3,319,027 Patented May 9, 1967 3,319,027 EN'CAPSULATED FUSE STRUCTURE FOR POLYPHASE CIRCUITS Paul C. Hitchcock, Plum Island, Mass, assignor to The Chase-Shawmut Company, Newburyport, Mass. Filed Jan. 26, 1965, Ser. No. 428,258 Claims. (Ql. 200-120) This invention is concerned with electric fuses, and more particularly with electric polyphase fuses.

Electric polyphase fuses are fuses comprising a plurality of fusible current paths, one for each phase of polyphase circuit, said plurality of fusible current paths being integrated into one single self-sustained structural unit. As a result of such integration, replacement of blown polyphase fuses is greatly simplified in comparison to the replacement of several single-phase fuses. Such simplification is of importance wherever minimizing downtime resulting from blowing of fuses in a polyphase circuit is a matter of critical nature.

It is one object of this invention to provide improved electric polyphase fuses and an improved method for manufacturing the same.

Another object of this invention is to provide improved electric polyphase fuses which are totally encapsulated in synthetic resin, and thus totally sealed off from the outer atmosphere, and do not emit any hot are products upon blowing thereof.

Another object of this invention is to provide an improved version of the fuses disclosed and claimed in the copending patent application of Frederick J. Kozacka, Compact Low-Voltage Power Fuses, filed Mar. 22, 1963, Ser. No. 267,193, assigned to the same assignee as the present invention.

Further objects of the invention and advantages thereof will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in which:

FIG. 1 is a side elevation of a pole unit for a polyphase fuse embodying this invention;

FIG. 2 is a side elevation of the structure of FIG. 1;

FIG. 3 is partly a longitudinal section and partly an elevation of a detail of the structure of FIGS. 1 and 2, namely of the blown fuse indicator thereof;

FIG. 4a is a top plan view of a housing for receiving three pole units of the kind shown in FIGS. 1 and 2;

FIG. 4b is a side elevation of the structure of FIG. 4a;

FIG. 40 is a bottom plan view of the structure of FIG. 4a;

FIG. 4d is a front view of the structure of FIG. 4a;

FIG. 5a is a side elevation of a sub-assembly including three pole units of the kind shown in FIGS. 1 and 2 and a housing of the kind shown in FIGS. 4a to 4d;

FIG. 5b is a front view of the structure of FIG. 5a;

FIG. 6 is a topplan view of a complete polyphase fuse embodying the present invention including the parts shown in the figures which have been referred to above;

FIG. 7 is substantially a section along 7 7 of FIG. 6; and

FIG. 8 is a side elevation of the structure of FIG. 6.

Referring now to the drawings, and more particularly to FIGS. 1 to 3 thereof, reference character 1 has been applied to indicate a pair of parallel stab contacts. Stab contacts 1 are formed by metal stampings which have a slightly larger spacing at their upper end than at their lower ends. A spacer 3 of insulating material in the form of a plate maintains the spacing between the upper ends of stab contacts 1. In addition to spacer 3 stab contacts 1 are also spaced by a spacer 4 in the form of a length of tubing of insulating material the ends of which engage the coaxial bores in stab contacts 1. The upper ends of stab contacts 1 are conductively interconnected by a pair of, or a pair of systems of, ribbon fuse links 5a and 5b. Ribbon fuse link 5a overlaps and physically engages the two edges of the stab contact 1 shown to the left of FIG. 2, and is spot-welded to these two edges. In a like fashion ribbon fuse link 5b overlaps and physically engages the two edges shown to the right of FIG. 2, and is spot welded to these two edges. Each fuse link 5a, 5b comprises five multi-perforated conductors forming parallel current paths. Hence stab contacts 1 are conductively interconnected by ten separate spaced current paths which may be readily deionized when substituted-following blowing of the fuse-by ten are columns in parallel. The way in which fuse links 5a, 5b are arranged in regard to, and secured to, stab contacts 1 allows to achieve this result in an extremely simple fashion.

The pole unit of FIGS. 1 and 2 further comprises a blown fuse indicator generally designated by the reference numeral 6. As shown in FIG. 3 blow fuse indicator 6 comprises an indicator pin 7 under the bias of a helical compression spring 9 arranged in a pin housing 8. Pin housing 8 is, in turn, arranged inside of a coaxial bushing 10 of insulating material. Pin housing 8 is mounted on the upper surface of insulating spacer 3, as clearly shown in FIGS. 1 and 2. Pin 7 is normally restrained by a pinre-straining wire 12 which is substantially V-shaped and forms a current path parallel to ribbon fuse links 5a, 5b having a relatively high resistance. The ends of restraining wire 12 are screwed at 11 against stab contacts 1, and the center portion of restraining wire 12 projects through a perforation (not shown) in spacer 3 into pin housing 8, and is attached to indicator pin 7. This normally precludes pin 7 from moving upwardly under the bias of spring 9.

Polyphase fuses according to this invention comprise a plurality of sub-assemblies of pole units of the kind illustrated in FIGS. 1-3, the number of such pole units being equal to the number of phases in the circuit to be protected. Thus a polyphase fuse for a three phase circuit comprises three pole units of the kind shown in FIGS. 1-3.

It will be apparent that occurrence of an excess current in any particular phase of a polyphase circuit causes fusion of the two ribbon link systems 5a, 5b pertaining to the respective pole unit and, as a result of kindling of arcs, substantial arc resistance is inserted into the particular phase. This establishes a voltage drop across restraining wire 12 and a current flow through the same sutficiently high to cause fusion of restraining wire 12. Upon fusion of restraining wire 12 pin 7 is propelled upwardly under the action of spring 9, thus indicating that the particular pole unit has blown.

The substantially prismatic housing 13 of FIGS. 4a to 4d is intended to receive three pole units of the kind shown in FIGS 1 to 3. Housing 13 is substantially rectangular in cross-section and comprises a bottom 13a and four lateral walls or side walls 13b arranged at right angles to each other to form a substantially rectangular prism. Bottom 13a is provided with three rectangular apertures or perforations to which reference character has been applied. Four legs or projections 13:: extend downwardly from bottom 13a of housing 13, each being substantially in the shape of a frustum of a cone. Grooves 13d inside of lateral walls 13b make it possible to readily subdivide housing '13 into a plurality, i.e. into three separate chambers by the insertion of partitions into said grooves. The bottom 13a of housing 13 may be provided with an internal boss 13f for reasons which will be explained below more in detail.

Housing 13 is intended to receive the upper ends of stab contacts 1 and the fuse links a, 5b and to allow the lower ends of stab contacts 1 to project outwardly through the apertures or perforations 130 in bottom 13a.

This arrangement of pairs of stab contacts 1 in housing 13 has been shown in FIGS. 5a and 5b. In these two figures reference characters P P and P have been applied to generally indicate three pole units of the kind illustrated in FIGS. 1 to 3, and described in connection therewith. The structure of FIGS. 5a and 5b comprises three parallel pairs of parallel stab contacts having upper ends inside of housing 13, and lower ends projecting through the aforementioned perforations 130 in the bottom 13a of housing 13 to the outside of housing 13. In order to secure the proper relative position of pole units P P and P inside of housing 13 these parts are arranged in an appropriate jig or fixture (not shown). Then a synthetic resin is cast into housing 13 up to the level H, and outside of housing 13, up to the level H, thus filling the space between the lower surface of bottom 13a and the lower ends of the legs 13c upon which housing 13 rests. In other words, a synthetic resin is poured into housing 13 and around the bottom 13a of the housing 13, encapsulating the entire bottom 13a and filling the empty spaces between perforations or cut-outs 130 of housing 13 and stab contacts 1. When this casting hardens, pole units P P and P are firmly held in their proper position inside of housing 13, and apertures or perforations 13c are entirely filled with synthetic resin. Reference numeral 14 has been applied in FIGS. 5a and 5b to designate the casting member enveloping the bottom 13a of housing 13, and locking pole units P P and P in position.

Casting member 14 is further used for positioning a pair of insulating tubings 15 extending at right angles to the general plane defined by the bottom 13a of housing 13, and defined by the horizontal surfaces of casting member 14. The purpose of tubings 15 will be explained below more in detail.

It is preferable to insert partitions or phase barriers 16 into the grooves 13d of housing 13 before making casting member '14, in which case partitions or phase barriers 16 will be firmly held in position by casting member 14.

It will be apparent that partitions 16 subdivide housing 13 into three fuse chambers of which each accommodates one of the pole units P P and P Each of these fuse chambers is intended to be filled with a pulverulent arc-quenching filler, preferably quartz sand. Reference character 17 has been applied in 'FIG. 7 to indicate the pulverulent arc-quenching filler which is being filled into the aforementioned fuse chambers after completion of casting member 14. Filler 17 is substantially level with the upper end of housing 13 or, in other words, but little space is left between the surface of the arcquenching filler 17 and the upper edge of housing 13. Filler 17 submerses entirely fusible elements 5a, 5b of each pole unit P P and P FIG. 7 clearly indicates that casting member 14 comprises a first portion situated inside of housing 13 engaging and being coextensive with the inner side of the bottom 13a thereof, and a second portion situated outside of housing 13 engaging and being coextensive with the outer side of bottom 13a, and that casting member 14 forms an annular projection 14a of rectangular shape surrounding housing 13 and projecting outwardly from the lateral walls 13b thereof.

Completion of the polyphase fuse structure calls for addition of another casting member of synthetic resin following filling of housing 13 with the pulverulent arcquenching material 17. Numeral 18 has been applied to indicate the last mentioned casting member which is particularly clearly shown in FIG. 7. Casting member 18 closes the side of housing 13 opposite the bottom 13a thereof, and is in physical contact with the upper surface of arc-quenching filler 17. Casting member 18 envelops the ouside of the lateral wall 13b of housing 13, and is flush with the upper surface of annular projection 14a,

i.e. with the surface of projection remote from the outer ends of stab contacts 1. The bushings 10" of blown fuse indicators 6 project transversely across the upper surface of casting member 18 and are therefore, held in position by the latter.

The aforementioned bosses 13 in housing 13 are a means making it possible to distinguish between different ratings of polyphase fuses having the same external appearance for causing rejection of fuses not having the required rating. A hole may be drilled through casting member 14 into bosses 13f intended to cooperate with a so-called rejection pin projecting from a fuse holder for receiving polyphase fuses, making it impossible to insert a fuse into the fuse holder unless the fuse has the required rating.

The aforementioned insulating tubes 15 define a pair of parallel ducts extending through casting member 18 and are intended to cooperate with pins in a fuse holder (not shown) in order to achieve perfect alignment of the fuse and the fuse holder when the former is inserted into the latter.

Housing 13 may be made of any suitable insulating material and of a synthetic resin, if desired. Casting members 14 and 18 must be made of compatible synthetic resins. They may be made of the same synthetic resin, e.g. an epoxy resin, and merge into a single unitary element or building block when the polyphase fuse is completed.

If housing 13 and castings 14 and 13 are made of the same material, these three parts may merge into one single unitary part upon completion of the polyphase fuse.

It will be understood that I have illustrated and described herein a preferred embodiment of my invention and that various alterations may be made in the details thereof without departing from the spirit and scope of the invention as set forth in the appended claims.

I claim as my invention:

1. A olyphase fusible protective device comprising in combination:

(a) a plurality of parallel pairs of parallel stab contacts having inner ends and having outer ends;

(b) a plurality of fusible element means each conductively interconnecting said inner ends of one of said plurality of pairs of stab contacts;

(c) a substantially prismatic housing receiving said plurality of fusible element means and said inner ends of said plurality of stab contacts, said housing including a bottom defining a plunality of apertures, each of said plurality of pairs of stab contacts projecting from the inside of said housing through one of said plurality of apertures to the outside of said housing;

((1) a first casting member of synthetic resin integral with said housing and including a portion situated inside said housing engaging and being coextensive with the inner surface of said bottom thereof and a second portion situated outside said housing engaging and being coextensive with the outer surface of said bottom thereof, said first casting member positioning said plurality of pairs of stab contacts relative tosaid housing;

(e) a pulverulent arc-quenching filler inside said housing for submersing said plurality of fusible elements;

(f) phase barrier means inside said housing arranged at right angles to said bottom thereof subdividing said pulverulent are-quenching filler into a plurality of separate bodies of pulverulent arc-quenching filler; and

(g) a second casting member of synthetic resin closing the side of said housing opposite said bottom thereof.

2. A polyphase fusible protective device comprising in combination:

(a) a plurality of parallel pairs of parallel stab contacts having inner ends and having outer ends;

(b) a plurality of fusible element means each conductively interconnecting said inner ends of one of said plurality of pairs of stab contacts;

(c) a substantially prismatic housing receiving said plurality of fusible element means and said inner ends of said plurality of stab contacts, said housing including a lateral wall and a bottom defining a plurality of apertures, each of said plurality of pairs of stab contacts projecting from the inside of said housing through one of said plurality of apertures to the outside of said housing;

(d) a first casting member of synthetic resin integral with said housing including a portion situated inside said housing engaging and being coextensive with the inner surface of said bottom thereof and a second portion situated outside said housing engaging and being coextensive with the outer surface of said bottom thereof, said first casting forming an annular projection of rectangular shape surrounding said housing and projecting outwardly from said lateral wall thereof, said first casting member positioning said plurality of pairs of stab contacts relative to said housing;

(e) a pulverulent arc-quenching filler inside said housing for submersing said plurality of fusible elements;

(f) phase barrier means inside said housing arranged at right angles to said bottom thereof subdividing said pulverulent arc-quenching filler into a plurality of separate bodies of pulverulent arc-quenching filler;

(g) a second casting member of synthetic resin integral with said housing closing the side of said housing opposite said bottom thereof, enveloping the outside of said lateral wall of said housing and being flush with the surface of said projection remote from said outer ends of said plurality of stab contacts.

3. A polyphase fusible device comprising in combination:

(a) a plurality of parallel pairs of parallel stab contacts having inner ends and having outer ends;

(b) a pair of spacer means of insulating materials each spacing one pair of said plurality of pairs of stab contacts;

(c) a plurality of fusible element means each conductively interconnecting said inner ends of one of said plurality of pairs of stab contacts;

((1) a plurality of blown fuse indicator pins each under the bias of one of a plurality of biasing springs and each under the control of one of a plurality of restraining wires conductively interconnecting said inner ends of one of said plurality of pairs of stab contacts;

(e) a substantially prismatic housing receiving said plurality of fusible elements and said inner ends of said plurality of stab contacts, said housing including a lateral Wall and a bottom defining a plurality of apertures, each of said plurality of pairs of stab contacts projecting from the inside of said housing through one of said plurality of apertures to the outside of said housing;

(f) a first casting member of synthetic resin integral with said housing including a portion situated inside said housing engaging and being coextensive with the inner surface of said bottom thereof and a second portion situated outside said housing engaging and being coextensive with the outer surface of said bottom there-of, said first casting forming an annular projection of rectangular shape surrounding said housing and projecting outwardly from said lateral Wall thereof,

said first casting member positioning said plurality of pairs of stab contacts relative to said housing;

(g) a pulverulent arc-quenching filler inside said housing for submersing said plurality of fusible elements;

(h) phase barrier means inside said housing arranged at right angles to the bottom thereof, subdividing said pulverulent arc-quenching filler into a plurality of separate bodies of pulverulent arc-quenching filler, said phase barrier means being fixedly positioned relative to said housing by said first casting member;

(i) a second casting member of synthetic resin integral with said housing closing the side of said housing opposite said bottom thereof, enveloping the outside of said lateral wall of said housing and being flush with the surface of said projection remote from said outer ends of said plurality of stab cont-acts; and

(j) a plurality of bushings each receiving one of said plurality of blown fuse indicator pins and each projecting from the inside of said housing transversely through the portion of said second casting member opposite said bottom of said housing and being held in position by said second casting member.

4. A method for manufacturing polyphase fusible protective devices comprising a plurality of parallel pairs of 25 stab contacts and a plurality of fusible means each conductively interconnecting ends of one of said plurality of pairs of stab contacts, said process comprising the steps of:

(a) threading the ends of said plurality of pairs of stab 30 contacts remote from the conductively interconnected ends thereof through the perforated bottom of a housing;

(b) surrounding the upper surface and the lower surface and the lower surface of said bottom of said housing with synthetic resin and filling synthetic resin into the gaps defined between said plurality of pairs of stab contacts and said bottom of said hous- 111g;

(c) curing said synthetic resin to lock said plurality of pairs of stab contacts in position relative to said housing;

(d) filling said housing with a pulverulent arc-quenching filler; and

(e) pouring a body of synthetic resin on the surface of said pulverulent arc-quenching filler and around the outer surface of the Wall of said housing.

5. A polyphase fusible protective device as specified in claim 3 wherein each of said plurality of indicator pins and each of the biasing springs thereof is arranged inside of an indicator housing resting with one end thereof on one of said plurality of spacer means, wherein each of said plurality of bushings projects with one end thereof into one of said plurality of separate bodies of arc-quench- 55 ing filler, and wherein said indicator pin housing of each of said plurality of indicator pins projects with one end thereof into one of said plurality of bushings.

References Cited by the Examiner UNITED STATES PATENTS 2,493,434 1/1950 Yonkers 29-1555 2,734,110 2/1956 Jacobs 200-120 2,830,156 4/1958 Burgess 200-120 2,834,852 5/1958 Swain et al. 200-120 3,029,328 4/1962 Kozacka 200-120 3,110,787 11/1963 Boizoni 200120 3,189,712 6/1965 Kozacka 200120 3,196,521 7/1965 Hollmann et al 29-155.5

BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner. 

1. A POLYPHASE FUSIBLE PROTECTIVE DEVICE COMPRISING IN COMBINATION: (A) A PLURALITY OF PARALLEL PAIRS OF PARLLEL STAB CONTACTS HAVING INNER ENDS AND HAVING OUTER ENDS; (B) A PLURALITY OF FUSIBLE ELEMENT MEANS EACH CONDUCTIVELY INTERCONNECTING SAID INNER ENDS OF ONE OF SAID PLURALITY OF PAIRS OF STAB CONTACTS; (C) A SUBSTANTIALLY PRISMATIC HOUSING RECEIVING SAID PLURALITY OF FUSIBLE ELEMENT MEANS AND SAID INNER ENDS OF SAID PLURALITY OF STAB CONTACTS, SAID HOUSING INCLUDING A BOTTOM DEFINING A PLURALITY OF APERTURES, EACH OF SAID PLURALITY OF PAIRS OF STAB CONTACTS PROJECTING FROM THE INSIDE OF SAID HOUSING THROUGH ONE OF SAID PLURALITY OF APERTURES TO THE OUTSIDE OF SAID HOUSING; (D) A FIRST CASTING MEMBER OF SYNTHETIC RESIN INTEGRAL WITH SAID HOUSING AND INCLUDING A PORTION SITUATED INSIDE SAID HOUSING ENGAGING AND BEING COEXTENSIVE WITH THE INNER SURFACE OF SAID BOTTOM THEREOF AND A SECOND PORTION SITUATED OUTSIDE SAID HOUSING ENGAGING AND BEING COEXTENSIVE WITH THE OUTER SURFACE OF SAID BOTTOM THEREOF, SAID FIRST CASTING MEMBER POSITIONING SAID PLURALITY OF PAIRS OF STAB CONTACTS RELATIVE TO SAID HOUSING; (E) A PULVERULENT ARC-QUENCHING FILLER INSIDE SAID HOUSING FOR SUBMERGING SAID PLURALITY OF FUSIBLE ELEMENTS; (F) PHASE BARRIER MEANS INSIDE SAID HOUSING ARRANGED AT RIGHT ANGLES TO SAID BOTTOM THEREOF SUBDIVIDING SAID PULVERULENT ARC-QUENCHING FILLER INTO A PLURALITY OF SEPARATE BODIES OF PULVERULENT ARC-QUENCHING FILLER; AND (G) A SECOND CASTING MEMBER OF SYNTHETIC RESIN CLOSING THE SIDE OF SAID HOUSING OPPOSITE SAID BOTTOM THEREOF. 